Modulated signaling system particularly applicable to wireless signaling



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MODULATED SIGNALING SYSTEM PARTICULARLY APPLICABLE TO WIRELESS SIGNALING Filed May 2, 1921 .2 shww-mwm 2 Fig.3.. N

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MWDULATED SIGNALING SYSTEM PARTICULARLY APPLICABLE TO WIRELESS SIGNALING.

Application filed may 2,

To all whom it may concern:

lle it known that T, NORMAN LEA, a British subject, and resident of 34/35 Norfolk Street, Strand, London, TV. C. 2, England, have invented certain new and useful Tmprovenients in ll-lodulated Signaling Systems Particularly Applicable to Wireless Signaling, of which the following is a specification.

This invention relates to modulated electric signaling systems and particularly to wireless signaling systems.

The principal object of'the invention is to provide an amplifying appliance wherein the high frequency output of an amplifying power valve energized by a suitable source of oscillating current is modulated by causing: the separately produced modulating p0- tentials to vary the potential of the grid of the power valve about a certain negative value and thus to vary' the high frequency output, of the valve.

in the accompanying drawings l igure 1 shows a circuit diagram of a power valve arranged for modulating currents of radio frequency or other frequencies.

T igure 2 shows a typical grid-potential anode-current characteristic curve of the power valve shown in Figure 1 and l igure 3 shows a diagram of a. wireless telephone transmittingcircuit.

Reterring now to Figure 1, the grid G of a thermionic valve V has a steady fixed negative potential applied thereto bv means of a suitable source such as battery B. The negative potential is of greater magnitude than that sufficient to reduce the anode current of the valve V to zero or a very small value. Upon the grid G are also impressed unrnodulatcd potentials supplied by a power source D and also modulating potentials supplied by a source M. The filament'of the valve l is heated by current from a source E. A source of electromotive force H and an output circuit LC are included in the anode circuit of the valve V. The output of the valve V will thus vary according to the modulating potentials supplied by M. The method of operation will be best followed hy reference to Figure 2 which shows a typical grid-.potential-anode-current characteristic curve of a three-electrode valve. The vertical axis YU represents the anode current and the horizontal axis XOX indi- 1921. Serial No. 466,205.

cates the grid potential. A steady negative potential is applied to the grid of. the valve V such that the normal or base-line potential will be more than sufiiciently negative to reduce the anode current of the power valve V to zero or to a very small value. The steady high frequency potentials applied to the grid by D will under these conditions produce substantially no output of current. For example, referring to Figure 2 it may be assumed that the grid potential due to the source E (Figure 1) is V and that the positive half-cycles of high frequency current supplied by D have an amplitude A. it will thus be seen that the representative point will travel along the horizontal foot of the characteristic curve but will not pass beyond ll Consequently the potentials suppliedby D will liberate no energy or practically none, in

the output circuit of the valve'l If however a positive potential of amplitude A is added to the grid, for example by a source M, the base line potential will be moved from V? to V and the oscillations from D will vary the grid potential about this new mean value V The positive half-cycles, as shown at A of modulating current will cause the ha -line potential to become less negative, the representative point travelling along the characteristic curve up to the point R so that a considerable amount of oscillatory energy will be liberated in the oscillating circuit LC of the power valve V.

The characteristic curve of the power valve should preferably be as shown with a sharp lower bend which is as close as possible to the zero current axis XUX. It is not essential that the characteristic curve should have the precise form indicated between its two bends, but any variation which is likely to. occur between these bends Wlll not prevent the operation of the valve according to the invention. The high frequency potentials are preferably of a magnitude not 1cm than that of the modulating potentials.

It will also he understood that the output of the valve V will depend on the amount of the characteristic curve traversed by the representive point during its excursion.

The oscillating potentials supplied by D will usually be of sufficiently great amplillllll tudc to enable as much as possible of the upwardly inclined portion of the charac llll) teristie curve to be used while the base line V will be in such a position that when these high frequency potentials are a plied to the grid, the output of the valve will be small or zero. Under these conditions the output will be approximately proportional to the modulating potentials. For the best results the high frequency potentials supby means of a transformer T. Modulating potentials are simultaneously applied to the which the circuit includes a battery 13 and the primary winding of a transformer T The secondary winding of this transformer T is in series with the secondary winding of the transformer T in the oscillatory circuit of the grid G. A fixed negative potential is given to the grid G by a suitable source such as. a battery B which is arranged in series with the secondary windings of the transformers T T. A condenser C shunts the secondary winding of the transformer T and the battery 13.

The output circuit of the valve V contains a source of high potential such as a battery H an inductance L coupled to an aerial N, a condenser C shunting the battery H and a connection to earth E. The potential of the battery 13 is preferably adjusted to such a valve that the arrangement operates in the manner described.

Although the method of operation of the invention has been explained with examples of circuital arrangements it will be understood that the invention-is not limited to any particular method or example hereinbefore described as many arrangements operating in the manner described are possible and will readily occur to those engaged in the art. 1

Having thus described 'my invention what I clalm as new and desire to secure by Let ters Patent. is 2- 1. In a radio telephone transmitting system includin a thermionic valve, means for modulating the electrical variations of the control electrode of said valve, said means comprising a source of unmodulated high frequency potentials, a modulating source of variable potential, and a source for supplying a fixed negative potential of greater magnitude than that suflicient to reduce'the anode current approximately to zero, said sources being connected to said control electrode.

2. In a radio telephone transmitting system including a thermionic valve, means for providing modulated continuous radio-frequency currents, said means comprising a source of unmodulated high frequency potentials, a source of low-frequency current, means connecting said sources to the grid circuit of the thermionic valve, and means. for applying a fixed negative potential of greater magnitude than that suflicient to reduce the anode current approximately to zero to the grid of the thermionic valve.

3. In a radio telephone transmitting system, the combination with a thermionic valve acting as an amplifier, of output and grid circuits associated with said valve, a source of high frequency potential connected to said grid, a source of microphonic potentials connected to said grid, and a source applying a fixed negative potential grid G by means of a microphone M of of greater magnitude than that sufiicient to reduce the anode current approximately to zero to said grid.

4. In a radio telephone transmitting system the combination with a thermionic va ve acting as an amplifier, of output and grid circuits associated with said valve, means for supplying high frequency oscillations to said grid, means for appl ing a fixed negative potential to said grid and means for varying the base line potential of the grid such that the positive half of the high frequency oscillations will travel along a greater portion of the upwardly inclined characteristic curve of the valve and thus liberate oscillatory energy in the output circuit of said valve, the output being normally in the neighborhood of zero when the modulating potentials are not applied.

5. In a high frequency wireless telephone system the combination with a thermionic valve of out ut and grid circuits associated with said "a ve, a source of high frequency oscillations, a transformer having primary and secondary windings, the primary winding being in series with said source of high frequency oscillations, whilst the secondary winding is in series with the grid circuit, a second transformer having primary and secondary windings, the secondary winding of the second transformer being in series with the grid circuit, a source for supplying a fixed negative potential of greater magnitude than that sufiicient to reduce the anode current approximately to zero in se-.

ries with the two secondary windings in the grid circuit, a condenser shunting the secondary winding of the second transformer and the source} for supplying the neonate which method consists in impressing upon said control electrode a source of negative lltl potential, adjusting said negative potential to a magnitude greater than that sudicient to reduce the anode current approximately. to zero and impressing upon said control electrode a series of high frequency impulses and a series of modulating impulses of difi'erent frequency.

7. A method of operating a thermionic amplifier having a cathode, an anode, a control electrode, input and output circuits and a source of current in said output circuit, which method consists in impressing upon said control electrode a fixed negative potential adjusted to a magnitude greater than that suficient to reduce the anode current approximately to zero and also impressing upon said control electrode a series 20 of impulses of radio frequency and a series of modulating impulses of audio freqpuency.

8. A method of operating a thermionic amplifier having a cathode, an anode, a control electrode, input and output circuits and a source of current in said output circuit, which method consists in applying a fixed negative potential to said control electrode of a magnitude such that the output of the amplifier is reduced substantially to zero, impressin a series of high frequency impulses to said control electrode and varying the base line potential of said control electrode such that the positive half of the high frequency impulses will travel along a greater portion of the upwardly inclined characteristic curve of the amplifier and thus, liberate oscillatory energy in the output circuit of the amplifier.

nonnau LEA. 

